External Monitor Issue After macOS Sequoia 15.1.1 Update

I ended up downgrading my Mac mini to Sonoma because of this. Tried Sequoia 15.1, same issue. As opposed to the Macbook, on the mini I've no alternative to using the external display, and the display going off while I type vigorously isn't exactly my idea of fun.

tkatebini wrote:

Thanks for this! Quick question: are you only running one external monitor, and not multiple? I was able to run 2 before, and with the update, now only one works, and only one is detected by my mac. No issues with my DELL windows laptop.

Which mac? And how are the displays connected to your mac?

Did you update DisplayLink software, if you use that?

arcyarcy wrote:

I now remembered what I did to fix the issue last time this happened after a MacOS update:

Power your monitor off and turn it on again.

Just tried that on the MacBook (the mini is already back on 14 and will stay there until Apple fixes this.) Powered off the monitor, removed cable (HDMI) from both sides, waited 5 minutes, then reconnected the cable on both ends, powered on the monitor and ... in less than 1 hour it flickered twice, the first time 2 minutes after I powered it on! I guess the MacBook is on its way to 14, too...

Same issue here - I can't connect my HDMI cable to a ASUS screen. The connection keeps turning on and off - it is just a endless loop, like 3 seconds between. I tried updating DisplayLink to the newest, didn't work... The monitor works on my Windows laptop...

Similar issue with an M1 Max MBP with 2 external displays. One external falls asleep while I'm actively working and the other external does not. Both were functioning perfectly prior to upgrading to Sequoia 15.1.1.

I could be wrong, of course, and I hope to be, but barring any interference, this looks like a hardware problem.

Disconnect any peripherals, and see if there is any change.

You could also try installing an older OS in an external drive, and see if that makes any difference.

Ok, I found a fix for me. It's all backward.

I had a "higher quality" / faster HDMI cable that I have been using fine for the last year with lower OS versions. During the general troubleshooting with Apple support, I remember I still had the old "Amazon basics" cable that I had used prior to the better-quality cable.

I swapped the old cable, and now it works fine.

"Newer Cable"

https://www.amazon.com/gp/product/B0CJLC72MG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

"Older Amazon Basic Cable"

https://www.amazon.com/gp/product/B083KX4F6K/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

An obvious culprit is that the old Amazon cable explicitly states the 60hz refresh rate while the newer cable lists higher refresh rates.

Now this has worked for a year so I think this suggests that there is something in the OS update that is forcing display connections closed if there is some sort of dissonance between the system refresh, connection, and display refresh.

At the end of the day I'd rather use my higher quality cable that has been good for the last year, but who knows when Apple will figure out this bug they introduced.

I have both a Viewsonic and a Samsung external and I see the issue in the Samsung. It’s pretty clearly a software quality issue unless a lot of displays from various manufacturers owned independently by users all over the country/world all failed coincidentally immediately following a software update from Apple.

This kind of stuff is why I never take X.0 releases from Apple anymore on any platform. The fact that this is happening in 15.1.1 just tells me the quality control has only gotten worse.

I have MacBook Pro 16" 2021 plus external monitor and iMac 2019 plus external monitor, both machines used for work in situations where a second monitor is essential. Both updated to Sequoia last week. No problems with the iMac external monitor but the MacBook external monitor keeps blacking out as described by others. It seems fine as long as I am working on something on that second screen but will disconnect itself when it hasn't been used for a few minutes. The only way to reconnect seems to be the classic unplug/replug and that doesn't always work.

I have no technical ability or available techie and it's really making life difficult and interrupting the workflow. When will Apple fix this?

Hi again,

Curious thing, with same computer, Macbook Pro 2018 Inter with T2Chip, the issue happens in one external TV, the one described in my previous post but it does NOT happens in another TV with same adapter, very weird.

This means that it does not happen to all monitors, it seems taht HDMI management has changed in some way that some vendors are not ready for?

Regards

The 15.2 update did not fix this issue for me. I only accepted the 15.1.1 update because I had a different issue related to iCloud synchronization of contact labels and Apple support insisted that I update to Sequoia. Now I have a new issue with my monitor while my original contact synch issue remains unresolved as well. Super cool!

This is still an issue on 15.2. I've updated my M3 Macbook Air and a portable monitor that worked fined before updating via the same USB-C cable, now it only gets power (I see the monitor splash screen) but does not connect to my MBA no matter what port I try, I've tried rebooting, resetting PRAM, nothing seems to work. One time it showed the display for 3 seconds after rebooting while leaving the monitor connected and then it went black again. Also it connects fine to a dock I have that's connected to 2 monitors (via DisplayLink) and it connects to a different monitor via DVI to USB-C cable without issue, (that monitor is powered though). Maybe the issue has to do with transmitting the display signal and power via one cable, but prior to the update it worked fine.

I have confirmed this is working with my M1 Macbook Pro with the same version of Sequoia 15.2, so it almost seems like it's a specific issue with a combination of MBA M3 hardware (potentially other models too) and 15.2. I hope they fix it soon, because it's very frustrating.

This is incredible!!

I updated to 15.2 and the issue dissapeared for almost 4 days, and now it happens again.... how is this possible?, I contacted apple and they told me they dont have notifications about similar issue regarding Sequoia....

I will uninstall Sequoia and will try Sonoma.

Janusromanus wrote:

This is incredible!!

I updated to 15.2 and the issue dissapeared for almost 4 days, and now it happens again.... how is this possible?, I contacted apple and they told me they dont have notifications about similar issue regarding Sequoia....

I suspect this is more of a corner case for them, given the amount of activity I see on this and similar threads. So they don't really care. I haven't been actively gathering data, but does this look like it's only happening with older external hardware? My monitor certainly is old and I've no intention to changing it, for sure not because of poor drivers from Apple...

I will uninstall Sequoia and will try Sonoma.

I've been back on Sonoma for 7 days now and even installed a security update. I've been fine so far, issue seems to be gone.

Exact same issue for me as OP. After updating to Sequoia 15.2 (I don't recall what the previous version was), the flickering issue occurred immediately after the update. Nothing else has changed about my set up after the update, so I feel very confident that the 15.2 update is the root of the issue.

Here's my set up prior to Sequoia 15.2 Update:

• Macbook M1 Max, 16-inch, 2021
• MacOS Sequoia 15 (not sure which previous version)
• External displays:
  • Working normally: "Display 1", LG 27GN650-B (connected via HDMI port)
  • Malfunctioning, flickering: "Display 2", LG 34UM69G-B (connected via usb-c port, USB-C to USB-C display cable)

Steps that failed to resolve issue:

• Follow steps 1-4 outlined here. Did not resolve issue.
  • Unplug cable and monitor power cord
  • Mac is already at latest update
  • Restart Mac
  • Change color profile of external monitor to Color LCD
  • Change refresh rate to 60 hz
  • Disabled true tone/night mode where applicable
• Changed USB-C cables, and tried plugging USB-c cable into different USB-c ports. Neither resolved issue
• Swapped display cable from USB-c/USB-c to USB-c/DisplayPort. Did not resolve issue.

Steps that resolved the issue so far as of Dec 19, 2024 at 11:06:

• Swap display cables between Display 1 (working) and Display 2 (malfunctioning):
  • Display 2 is now connected via HDMI cable to mac HDMI port
    • Color profile: Color LCD, 60 Hz refresh rate, no true tone/night
  • Connect Display 1 via DisplayPort to USB-C mac port

Since swapping display cables between external monitors, the flickering has stopped. I will update accordingly if anything changes.